Musculoskeletal Growth/Injury and Repair - Nerve Flashcards
Peripheral Nerve Injuries are also known as what?
Lower Motor Neurone Injuries
what makes up a peripheral nerve?
- Motor unit (efferent)
- Sensory unit
- Spinal Nerves
what makes up the motor unit (efferent)
anterior horn cell, (located in the gray matter of the spinal cord)
motor axon,
muscle fibres (neuromuscular junctions)
what makes up the sensory unit?
cell bodies in posterior root ganglia
I.e. lie outside the spinal cord
nerve fibres join to form what?
anterior (ventral) motor roots
posterior (dorsal) sensory roots
what makes up spinal nerves?
Anterior and posterior roots combine to form a spinal nerve
Exit the vertebral column via an intervertebral foramen
what are the featuresof a peripheral nerve?
- The part of a spinal nerve distal to the nerve roots
- Bundles of nerve fibres
- Range in diameter from 0.3-22 μm
- Schwann cells form a thin cytoplasmic tube around
- Larger fibres in a multi-layered insulating membrane (myelin sheath)
- Multiple layers of connective tissue surrounding axons
Structure:
• peripheral nerve is a highly organised structure comprised of nerve fibres, blood vessels and connective tissue
- AXONS (long processes of neurones) are coated with __________ and grouped into
- FASCICLES (nerve bundles ) covered with __________; these are grouped to form the
- NERVE which is covered with __________
endoneurium
perineurium
epineurium
anatomy - structure:
- neurone (nerve cell), surrounded by _________ cell
- bundles
Schwann
what are the different Fiber types and functions (from largest to smallest)?
Increasing size = increasing speed of transmission
what are the different types of injury that can occur to a nerve?
- compression (at different possible levels) [refer: lecture “Nerve palsies in the limbs”]
- trauma - direct (blow, laceration) or indirect (avulsion, traction)
- neurapraxia
- axonotmesis
- neurotmesis
compression - entrapment
what are some classical conditions seen?
Carpal tunnel syndrome - Median nerve at wrist
Sciatica - Spinal root by intervertebral disc
Morton’s neuroma - (digital nerve in 2nd or 3rd web space of forefoot)
what are the 3 different types of trauma?
neurapraxia
axonotmesis
neurotmesis
what is neurapraxia?
nerve in continuity
stretched (8% will damage microcirculation) or bruised
reversible conduction block - local ischaemia and demyelination
prognosis good (weeks or months)
Neurapraxia is a disorder of the peripheral nervous system in which there is a temporary loss of motor and sensory function due to blockage of nerve conduction, usually lasting an average of six to eight weeks before full recovery
what is axonotmesis?
endoneurium intact (tube in continuity), but disruption of axons; more severe injury
stretched ++ (15% elongation disrupts axons) or crushed or direct blow
Wallerian degeneration follows
prognosis fair (sensory recovery often better than motor - often not normal but enough to recognise pain, hot & cold, sharp & blunt)
The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact
can peripheral nerves regenerate?
yes
what is neurotmesis?
complete nerve division
laceration or avulsion
no recovery unless repaired (by direct suturing or grafting)
endoneural tubes disrupted so high chance of “miswiring” during regeneration
prognosis poor
most serious nerve injury in the scheme. In this type of injury, both the nerve and the nerve sheath are disrupted. While partial recovery may occur, complete recovery is impossible
summary picture showing the different types of truma
Neurapraxia – axon in tact but just one area not working
Axonotmesis – axon has disappeared and will have to grow down endoneurial tube
Neurotmesis – different severities, so may just have endoneurium disrupted, perineurial destruction and epineural destruction and indicate different prognosis’s
what is a clsoed nerve injury?
- Associated with nerve injuries in continuity - neuropraxis and axonotmesis
- spontaneous recovery is possible
- surgery indicated after 3 months - if no recovery is identified, Clinical or Electromyography
- axonal growth rate (1–3 mm/day)
- Examples - Typically stretching of nerve, brachial plexus injuries or Radial Nerve humeral fracture
what is an open nerve injury?
- Frequently related to nerve division, neurotmetic injuries E.g. knives/glass
- Treated with early surgery
- Distal portion of the nerve undergoes Wallerian degeneration - Occurs up 2 to 3 weeks after the injury
(wallerian degeneration - active process of degeneration that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury (i.e. farther from the neuron’s cell body) degenerates)
Injury - clinical features
what are some sensory features?
dysaethesiae (disordered sensation)
anaesthetic (numb), hypo- & hyper-aesthetic, paraesthetic (pins & needles)
Injury - clinical features
what are some motor features?
paresis (weakness) or paralysis ± wasting
dry skin - loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin
Injury - clinical features
what are some reflex features?
diminished or absent
what is the process of nerves healing?
- very slow!!
- starts with initial death of axons distal to site of injury - Wallerian degeneration - then degradation myelin sheath
- proximal axonal budding occurs after about 4 days
helaing - regeneration proceeds at rate of about what?
regeneration proceeds at rate of about 1 mm/day (or 1 inch/month) - poss. 3-5 mm/day in children
what is the first modality to return in healing nerves?
pain
prognosis for recoverey depends on what?
•whether nerve is
–“pure” (only sensory or only motor)
–“mixed” (both sensory and motor within same nerve)
•how distal the lesion is (proximal worse)
Mixed nerve have a varied recovers as the nerves can recover down the wrong tubes
If it is a long way back to grow end plate may not still be functioning
how can injury and recovery be monitored?
- Tinel’s sign can monitor recovery - (tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed)
- Injury can be assessed, and recovery monitored - by electrophysiological Nerve Conduction Studies
how is nerve repair done?
• Direct Repair
- Laceration - 2 ends clsoe together
- No loss nerve tissue
- Microscope/Loupes
- Bundle repair
- Growth factors
• Nerve Grafting (when ends cant be pulled together)
- Nerve loss
- Late repair - (retraction), Sural nerve
THE “RULE OF THREE”
Surgical timing in a traumatic peripheral nerve injury
what is it?
- Immediate surgery within 3 days for clean and sharp injuries
- Early surgery within 3 weeks for blunt/contusion injuries
- Delayed surgery, performed 3 months after injury, for closed injuries
Peripheral or Central nerve injury? how do you tell?
- Peripheral nerve injuries may result in loss of motor function, sensory function, or both
- Injuries to the central nervous system may cause loss of motor function, sensory function, or both
- How do I tell the difference clinically?
Where there is no or limited muscle stimulation the muscle will atrophy so in UMN there is increased in tone and activity atrophy is absent
